> For the complete documentation index, see [llms.txt](https://vijaynarayanan24.gitbook.io/art-of-software-reuse/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://vijaynarayanan24.gitbook.io/art-of-software-reuse/design/operability.md).

# Supportability

There is an expanded set of capabilities that are also necessary when addressing non-functional requirements – those that are very relevant specially when your reusable component or service grows in popularity and usage. They fall under two categories: operational agility and fault-tolerance. Here are a few candidate capabilities in both these categories:

Operational Agility / Supportability:

* Ability to enable / disable both services and operations within a service
* Ability to provision additional service instances based on demand (elastic scaling)
* Maintenance APIs for managing resources (reset connection pool, individual connections, clear cached data, etc.)
* Ability to view Service APIs that are breaching and ones that are the risk of breaching operational SLAs
* Model and detect out of band behavior with respect to resource consumption, transaction volumes, usage trends during a time period etc.

Fault Tolerance:

* Failing fast when there is no point executing operations partially
* Ability to detect denial of service attacks from malicious clients
* Ability to gracefully handle unexpected usage spikes via load shedding, re-balancing, deferring non-critical tasks, etc.
* Detecting failures that impact individual operations as well as services as a whole
* Dealing with unavailable downstream dependencies
* Leveraging time outs when integrating with one or more dependencies
* Automatically recovering from component failures

It is also important to point out that both these aspects are heavily interconnected and influence each other.